pentagonal /pɛnˈtæɡənəl/adjective 1noun 1forms 3 adjective1 •Of, relating to, or shaped like a pentagon.Seed micromorphology:—Seed coat is laticostate. Epidermal cells are elliptical to irregularly pentagonal. Cell walls are thickened mostly at the corners, the boundaries are raised […] — 2018 noun1 •Something having the shape of a pentagon.Speaking of protection, note that not only are the end pentagonals surrounded by a generous air space, but the entire instrument is insulated, […] — 1941 formspentagonals · more pentagonal · most pentagonal